ssrs qr code free TeamLRN in Software

Create EAN13 in Software TeamLRN

TeamLRN
Recognize EAN-13 In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Making GTIN - 13 In None
Using Barcode generator for Software Control to generate, create EAN13 image in Software applications.
CHAP. 12]
Recognize EAN-13 Supplement 5 In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
GS1 - 13 Printer In Visual C#.NET
Using Barcode creator for Visual Studio .NET Control to generate, create European Article Number 13 image in Visual Studio .NET applications.
COMPOSITION AND INHERITANCE
Make EAN 13 In Visual Studio .NET
Using Barcode creation for ASP.NET Control to generate, create GTIN - 13 image in ASP.NET applications.
EAN-13 Maker In .NET
Using Barcode encoder for .NET framework Control to generate, create EAN-13 Supplement 5 image in VS .NET applications.
f() gets executed: X::f() or Y::f() The answer is that p->f() will execute X::f() because p had type X*. The fact that p happens to be pointing at that moment to an instance of subclass Y is irrelevant; it s the statically defined type X* of p that normally determines its behavior.
Create EAN13 In VB.NET
Using Barcode maker for .NET framework Control to generate, create EAN-13 image in .NET applications.
Making Barcode In None
Using Barcode creator for Software Control to generate, create bar code image in Software applications.
EXAMPLE 12.10 Using virtual Functions
Encoding UPC-A In None
Using Barcode drawer for Software Control to generate, create UPC-A Supplement 5 image in Software applications.
Draw ANSI/AIM Code 39 In None
Using Barcode creation for Software Control to generate, create Code 3 of 9 image in Software applications.
This demo program declares p to be a pointer to objects of the base class X. First it assigns p to point to an instance x of class X. Then it assigns p to point to an instance y of the derived class Y. class X { public: void f() { cout << "X::f() executing\n"; } };
EAN / UCC - 14 Creator In None
Using Barcode maker for Software Control to generate, create GS1 128 image in Software applications.
Encoding Bar Code In None
Using Barcode creation for Software Control to generate, create bar code image in Software applications.
class Y : public X { public: void f() { cout << "Y::f() executing\n"; } }; int main() { X x; Y y; X* p = &x; p->f(); // invokes X::f() because p has type X* p = &y; p->f(); // invokes X::f() because p has type X* } X::f() executing X::f() executing
Draw International Standard Book Number In None
Using Barcode drawer for Software Control to generate, create ISBN image in Software applications.
Scan Code 128 Code Set C In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
Two function calls p->f() are made. Both calls invoke the same version of f() that is defined in the base class X because p is declared to be a pointer to X objects. Having p point to y has no effect on the second call p->f(). Transform X::f() into a virtual function by adding the keyword virtual to its declaration: class X { public: virtual void f() { cout << "X::f() executing\n"; } }; With the rest of the code left unchanged, the output now becomes
Data Matrix ECC200 Maker In None
Using Barcode printer for Office Excel Control to generate, create Data Matrix 2d barcode image in Office Excel applications.
Code-39 Encoder In Java
Using Barcode generator for Android Control to generate, create Code 39 Full ASCII image in Android applications.
X::f() executing Y::f() executing
Generate Bar Code In .NET
Using Barcode creator for VS .NET Control to generate, create barcode image in Visual Studio .NET applications.
Code 128 Code Set A Creation In Java
Using Barcode encoder for Android Control to generate, create Code 128 Code Set A image in Android applications.
Now the second call p->f() invokes Y::f() instead of X::f().
Generating Matrix Barcode In Java
Using Barcode generator for Java Control to generate, create Matrix Barcode image in Java applications.
Encoding GS1 128 In Java
Using Barcode printer for Eclipse BIRT Control to generate, create EAN / UCC - 14 image in BIRT reports applications.
This example illustrates polymorphism: the same call p->f() invokes different functions. The function is selected according to which class of object p points to. This is called dynamic binding because the association (i.e., binding) of the call to the actual code to be executed is deferred until run time. The rule that the pointer s statically defined type determines which member function gets invoked is overruled by declaring the member function virtual. Here is a more realistic example:
COMPOSITION AND INHERITANCE
[CHAP. 12
EXAMPLE 12.11 Polymorphism through virtual Functions
Here is a Person class with a Student subclass and a Professor subclass: class Person { public: Person(char* s) { name = new char[strlen(s)+1]; strcpy(name, s); } void print() { cout << "My name is " << name << ".\n"; } protected: char* name; };
class Student : public Person { public: Student(char* s, float g) : Person(s), gpa(g) { } void print() { cout << "My name is " << name << " and my G.P.A. is " << gpa << ".\n"; } private: float gpa; }; class Professor : public Person { public: Professor(char* s, int n) : Person(s), publs(n) { } void print() { cout << "My name is " << name << " and I have " << publs << " publications.\n"; } private: int publs; }; int main() { Person* p; Person x("Bob"); p = &x; p->print(); Student y("Tom", 3.47); p = &y; p->print(); Professor z("Ann", 7); p = &z; p->print(); } My name is Bob. My name is Tom. My name is Ann.
The print() function defined in the base class is not virtual. So the call p->print() always invokes that same base class function Person::print() because p has type Person*. The pointer p is statically bound to that base class function at compile time. Now change the base class function Person::print() into a virtual function, and run the same program:
TeamLRN
CHAP. 12]
COMPOSITION AND INHERITANCE
class Person { public: Person(char* s) { name = new char[strlen(s+1)]; strcpy(name, s); } virtual void print() { cout << "My name is " << name << ".\n"; } protected: char* name; }; My name is Bob. My name is Tom and my G.P.A. is 3.47 My name is Ann and I have 7 publications.
Now the pointer p is dynamically bound to the print() function of whatever object it points to. So the first call p->print() invokes the base class function Person::print(), the second call invokes the derived class function Student::print(), and the third call invokes the derived class function Professor::print(). We say that the call p->print() is polymorphic because its meaning changes according to circumstance.
In general, a member function should be declared as virtual whenever it is anticipated that at least some of its subclasses will define their own local version of the function. 12.8 VIRTUAL DESTRUCTORS Virtual functions are overridden by functions that have the same signature and are defined in subclasses. Since the names of constructors and destructors involve the names of their different classes, it would seem that constructors and destructors could not be declared virtual. That is indeed true for constructors. However, an exception is made for destructors. Every class has a unique destructor, either defined explicitly within the class definition or implicitly by the compiler. An explicit destructor may be defined to be virtual. The following example illustrates the value in defining a virtual destructor: EXAMPLE 12.12 Memory Leaks
This program is similar to Example 12.6: class X { public: X() { p = new int[2]; cout << "X(). "; } ~X() { delete [] p; cout << "~X().\n"; } private: int* p; };
class Y : public X { public: Y() { q = new int[1023]; cout << "Y(): Y::q = " << q << ". ~Y() { delete [] q; cout << "~Y(). "; } private: int* q; };
"; }
Copyright © OnBarcode.com . All rights reserved.